(a) Field of the Invention
The present invention relates to a fuel cell stack. More particularly, the present invention relates to a fuel cell stack that improves a distribution deviation of a reaction gas of unit cells.
(b) Description of the Related Art
In general, a fuel cell system is a kind of electric generation system that generates electrical energy through an electrochemical reaction of a fuel (e.g., hydrogen) and an oxidant (e.g., oxygen). As the need for environmentally friendly vehicles grows, fuel cells have begun to be implemented in the vehicles as an alternate source of energy. These types of vehicles are known in the industry as fuel cell vehicles.
One type of fuel cell is a hydrogen fuel cell system, this type of fuel cell system includes a fuel cell stack, a hydrogen supply unit that supplies hydrogen to the fuel cell stack, an air supply unit that supplies air to the fuel cell stack, and a heat/water management device that removes water and a reaction heat of the fuel cell stack. This heat/water management device also controls the operation temperature of the fuel cell stack.
The fuel cell stack is formed as an electrical generator unit or stack in which tens to hundreds of unit cells are consecutively arranged. In this configuration, unit cells are defined by separators on both sides thereof and provided with a membrane-electrode assembly (MEA) interposed therebetween the separators.
Additionally, once a sufficient number of unit cells are stacked together, end plates are installed on the outermost ends (both sides) of the consecutively stacked unit cells. These end plates press attach to the outermost unit cell and press the plurality of unit cells together to form the fuel cell stack.
Furthermore, at a separator of unit cells, a manifold for supplying and exhausting a reaction gas (e.g., hydrogen and air) and a coolant is formed. Typically, at one of end plates a reaction gas inlet and outlet that are connected to the manifold are formed as well. Therefore, any reaction gas that is supplied to the reaction gas inlet of the end plate flows along the manifold and is supplied to the unit cells accordingly, and any reaction gas that remains after being supplied to the unit cells flows along another manifold and is exhausted through the reaction gas outlet of the other end plate.
In this process, the fuel cell stack generates electrical energy through an electrochemical reaction of hydrogen and air. However, as the supply of reaction gas moves through the plurality of unit cells, a flux deviation essentially occurs in a supply fluid between unit cells. In particular, as the reaction gas recedes from the inlet side of unit cells, a reaction gas of a flux less than a reference flux may be injected into unit cells.
This distribution deviation occurs in a reaction gas because that the pressure differentials that are applied to each unit cell are the same, but as a reaction gas recedes from the inlet, an additional pressure differential that is applied to the manifold occurs.
Further, in the fuel cell stack, during initial operation, at the reaction gas inlet side, an excess amount of condensed water is generated. As such, condensed water, having a density higher than that of a reaction gas, moves toward unit cells of the reaction gas inlet side of the fuel cell stack.
Disadvantageously, a distribution deviation of a reaction gas in the fuel cell stack may cause a cell omission phenomenon in unit cells to which a reaction gas of a flux less than a reference flux is supplied or may deteriorate the durability performance of the fuel cell stack. Additionally, the supply flux of a reaction gas cannot be optimized and thus a performance of the fuel cell stack may be deteriorated as well. Further, in a reaction gas distribution structure of the fuel cell stack, flooding from condensed water within unit cells of the reaction gas inlet side may also occur.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.